The invention concerns a usage application of a continuous-operation machine, consisting essentially of a horizontally positioned cylindrical container having a product feed chute and a product exit chute, a driveable shaft in the container, preferentially mounted to front walls, tools mounted on the shaft, which are directed radially outward from the shaft, whereby the shaft is operated in the Froude number region FR.gtoreq.7.
A continuous-operation machine of this type has become known through the brochure "Befeuchtungsmischer" (wetting-mixer) WD 12.79 SM/Rd-e 47.1500 Gebruder Lodige Maschinenbau GmbH, Paderborn, Germany, 1979.
The known rapid continuous-operation and compact machine is designed for large through-put. It processes, as is known in the art, powdered and short-fibered material with liquid media and is utilized in the area of solid-liquid mixing. The known machine is distinguished, on the one hand, by a good mixing precision at short dwell times and large through-put capacities are possible with small machine dimensions.
The tools mounted onto the shaft rotate in a Froude number range of 7-20, whereby the Froude number is formed from the quotient of the revolution frequency n and the critical revolution frequency n.sub.c. ##EQU1##
In this revolution frequency range the product flowing into the machine is subjected to centrifugal forces by the tools which press the product against the inner wall of the container. The product passes through the machine in a product-cycle. In this fashion, the known mixing processes occur.
When manufacturing gypsum plaster board, a certain amount of unmarketable waste always occurs which consists essentially of damaged board or board which is not to specifications. The waste occurs partially directly following binding or sealing, and partially after drying of the bound boards. In the first case the waste comprises 30 to 40% moisture and in the second case the waste material is practically completely dry. The amount of waste material depends on the particular manufacturing procedure and differs; this amount lies in general between 2 and 8% of the product bulk and reaches, in extreme cases, even 10%.
In practice the re-introduction of this waste as a secondary raw material back into the production process is known in the art. Towards this end one had initially coarsely pulverized the boards. This pre-pulverized material is a mixture between gypsum chips and cardboard shreds assuming sizes up to the size of a hand on which gypsum residue is firmly bonded. With the gypsum plaster boards which are most often used having an areal weight of approximately 8 kilograms per m.sup.2, the fraction of paper is between 4.5 to 5%, and with boards having an areal weight of approximately 11 kilograms per m.sup.2, from 3.4 to 3.8%. A practically acceptable separation of the paper and the gypsum, for example by sorting, has, up to this point, not been successfully implemented in technical production.
The coarse pre-pulverized material cannot be processed in the conventional calcination devices. The paper shreds would, in for example an indirectly heated rotating pipe calcination device, float upon the gypsum grain bed to form balls which cannot be properly withdrawn and which, therefore, can clog the calcination device. There is also the risk that, when emptying the calcination device, dried paper remains in the calcination device which, when repowering up, causes an explosion.
One had also introduced the coarsely pre-pulverized material together with fresh natural gypsum into a mill. The up to 30 mm large natural gypsum chips effect, in advantageous cases, a certain further pulverization of the shredded paper which, however, is not always sufficient. If small grain flue-gas gypsum or chemical gypsum is utilized as a raw material a satisfactory further pulverization is not possible. The procedure has, therefore, not been practically successful.